Reconstitution of pyrroloquinoline quinone-dependent D-glucose oxidase respiratory chain of Escherichia coli with cytochrome o oxidase

Escherichia coli membrane-bound glucose dehydrogenase (mGDH), which is one of quinoproteins containing pyrroloquinoline quinone (PQQ) as a coenzyme, is a good model for elucidating the function of bound quinone inside primary dehydrogenases in respiratory chains. Enzymatic analysis of purified mGDH from cells defective in synthesis of ubiquinone (UQ) and/or menaquinone (MQ) revealed that Q-free mGDH has very low levels of activity of glucose dehydrogenase and UQ 2 reductase compared with those of UQ-bearing mGDH, and both activities were significantly increased by reconstitution with UQ 1 . On the other hand, MQ-bearing mGDH retains both catalytic abilities at the same levels as those of UQ-bearing mGDH. A radiolytically generated hydrated electron reacted with the bound MQ to form a semiquinone anion radical with an absorption maximum at 400 nm. Subsequently, decay of the absorbance at 400 nm was accompanied by an increase in the absorbance at 380 nm with a first order rate constant of 5.7 ؋ 10 3 s ؊1 . This indicated that an intramolecular electron transfer from the bound MQ to the PQQ occurred. EPR analysis revealed that characteristics of the semiquinone radical of bound MQ are similar to those of the semiquinone radical of bound UQ and indicated an electron flow from PQQ to MQ as in the case of UQ. Taken together, the results suggest that MQ is incorporated into the same pocket as that for UQ to perform a function almost equivalent to that of UQ and that bound quinone is involved at least partially in the catalytic reaction and primarily in the intramolecular electron transfer of mGDH.Facultative anaerobic bacteria and lower eukaryotes are known to have capabilities to adapt to environmental changes for survival. One such capability is acquired by synthesis of both UQ 2 and MQ(1). A fine control of biosynthesis and the relative concentrations of the two Qs is crucial for growth, in respect to oxygen supply under aerobic and anaerobic conditions (2-5). UQ n as an electron carrier is primarily involved in aerobic respiration, whereas MQ n is involved in anaerobic respiration. Bekker et al.(6) reported significant changes in both size and redox state of the Q pool when the environment changes from a well aerated environment to an environment with low oxygen availability. Some respiratory components that intrinsically interact with Q are capable of catalyzing redox reactions with both UQ and MQ (7-11). Such interactions may be important in physiological and evolutionary aspects in addition to enzymatic function. DsbB, which is involved in the formation of disulfide bonds in Escherichia coli extracytoplasmic space, and fumarate reductase differentially employ Q under aerobic and anaerobic conditions (7-9). The respiratory oxidation in E. coli of ␣-glycerophosphate and D-lactate is promoted by both UQ and MQ, whereas NADH oxidase and succinate oxidase require only UQ for activity (12).E. coli membrane-bound mGDH, which is known as a quinoprotein, catalyzes the oxidation of D-glucose to D-gluconate at the periplas...

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Menaquinone as Well as Ubiquinone as a Bound Quinone Crucial for Catalytic Activity and Intramolecular Electron Transfer in Escherichia coli Membrane-bound Glucose Dehydrogenase

Mustafa

Migita

Ishikawa

et al. 2008

“…The Escherichia coli membrane-bound glucose dehydrogenase (mGDH) 2 belongs to the quinoprotein family with PQQ as a coenzyme (1,2), and it catalyzes D-glucose oxidation to D-gluconate at the periplasmic side to transfer electrons to ubiquinol oxidase via UQ in the respiratory chain (3)(4)(5). Topological analysis revealed that mGDH consists of an N-terminal hydrophobic domain with five membrane-spanning segments and a large C-terminal domain residing in the periplasm, which contains PQQ and Ca 2ϩ -or Mg 2ϩ -binding sites in a superbarrel structure, conserved in quinoproteins (6 -8).…”

mentioning

confidence: 99%

Amino Acid Residues Interacting with Both the Bound Quinone and Coenzyme, Pyrroloquinoline Quinone, in Escherichia coli Membrane-bound Glucose Dehydrogenase

Mustafa

Ishikawa

Kobayashi

et al. 2008

The Escherichia coli membrane-bound glucose dehydrogenase (mGDH) as the primary component of the respiratory chain possesses a tightly bound ubiquinone (UQ) flanking pyrroloquinoline quinone (PQQ) as a coenzyme. Several mutants for Asp-354, Asp-466, and Lys-493, located close to PQQ, that were constructed by site-specific mutagenesis were characterized by enzymatic, pulse radiolysis, and EPR analyses. These mutants retained almost no dehydrogenase activity or ability of PQQ reduction. CD and high pressure liquid chromatography analyses revealed that K493A, D466N, and D466E mutants showed no significant difference in molecular structure from that of the wild-type mGDH but showed remarkably reduced content of bound UQ. A radiolytically generated hydrated electron (e aq ؊ ) reacted with the bound UQ of the wild enzyme and K493R mutant to form a UQ neutral semiquinone with an absorption maximum at 420 nm. Subsequently, intramolecular electron transfer from the bound UQ semiquinone to PQQ occurred. In K493R, the rate of UQ to PQQ electron transfer is about 4-fold slower than that of the wild enzyme. With D354N and D466N mutants, on the other hand, transient species with an absorption maximum at 440 nm, a characteristic of the formation of a UQ anion radical, appeared in the reaction of e aq ؊ , although the subsequent intramolecular electron transfer was hardly affected. This indicates that D354N and D466N are prevented from protonation of the UQ semiquinone radical. Moreover, EPR spectra showed that mutations on Asp-466 or Lys-493 residues changed the semiquinone state of bound UQ. Taken together, we reported here for the first time the existence of a semiquinone radical of bound UQ in purified mGDH and the difference in protonation of ubisemiquinone radical because of mutations in two different amino acid residues, located around PQQ. Furthermore, based on the present results and the spatial arrangement around PQQ, Asp-466 and Lys-493 are suggested to interact both with the bound UQ and PQQ in mGDH.The Escherichia coli membrane-bound glucose dehydrogenase (mGDH) 2 belongs to the quinoprotein family with PQQ as a coenzyme (1, 2), and it catalyzes D-glucose oxidation to D-gluconate at the periplasmic side to transfer electrons to ubiquinol oxidase via UQ in the respiratory chain (3-5). Topological analysis revealed that mGDH consists of an N-terminal hydrophobic domain with five membrane-spanning segments and a large C-terminal domain residing in the periplasm, which contains PQQ and Ca 2ϩ -or Mg 2ϩ -binding sites in a superbarrel structure, conserved in quinoproteins (6 -8). Although its tertiary structure has not been resolved, the arrangement of amino acid residues around PQQ has been modeled on the basis of the crystal structure of the quinoprotein methanol dehydrogenase (6) as depicted in Fig. 1. The arrangement has been confirmed by results of several experiments with site-directed amino acid substitutions (9 -13). The orthoquinone portion of PQQ is a vital part for the catalytic reaction, to which Lys-493 hydr...

“…However, the biologically active pigment prodigiosin is inhibited by growth in glucose-rich medium (43). Quinoprotein glucose dehydrogenase uses PQQ as a cofactor, and its substrates are D-glucose and ubiquinone, a component of the electron transport chain (44,45). S. marcescens glucose dehydrogenase (GdhS) was previously shown to require PQQ for glucose dehydrogenase activity (46).…”

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confidence: 99%

Crystal Structure and Function of PqqF Protein in the Pyrroloquinoline Quinone Biosynthetic Pathway

Wei

Ran

et al. 2016

Pyrroloquinoline quinone (PQQ) has received considerable attention due to its numerous important physiological functions. PqqA is a precursor peptide of PQQ with two conserved residues: glutamate and tyrosine. After linkage of the C␥ of glutamate and C⑀ of tyrosine by PqqE, these two residues are hypothesized to be cleaved from PqqA by PqqF. The linked glutamate and tyrosine residues are then used to synthesize PQQ. Here, we demonstrated that the pqqF gene is essential for PQQ biosynthesis as deletion of it eliminated the inhibition of prodigiosin production by glucose. We further determined the crystal structure of PqqF, which has a closed clamshell-like shape. The PqqF consists of two halves composed of an N-and a C-terminal lobe. The PqqF-N and PqqF-C lobes form a chamber with the volume of the cavity of ϳ9400 Å 3 . The PqqF structure conforms to the general structure of inverzincins. Compared with the most thoroughly characterized inverzincin insulin-degrading enzyme, the size of PqqF chamber is markedly smaller, which may define the specificity for its substrate PqqA. Furthermore, the 14-amino acid-residue-long tag formed by the N-terminal tag from expression vector precisely protrudes into the counterpart active site; this N-terminal tag occupies the active site and stabilizes the closed, inactive conformation. His-48, His-52, Glu-129 and His-14 from the N-terminal tag coordinate with the zinc ion. Glu-51 acts as a base catalyst. The observed histidine residue-mediated inhibition may be applicable for the design of a peptide for the inhibition of M16 metalloproteases.Pyrroloquinoline quinone (PQQ), 4 an aromatic orthoquinone, has been recognized as the third class of redox cofactors in addition to the well known cofactors, nicotinamide (NAD(P) ϩ ) and flavin (FAD, FMN) (1). PQQ was first identified from methanol dehydrogenase in methylotrophic bacteria (2), and several bacterial dehydrogenases, such as glucose dehydrogenases, quinate dehydrogenase, and alcohol dehydrogenase, were later found to be quinoproteins (3-5). Recently, sugar oxidoreductase in the basidiomycete Coprinopsis cinerea (6), 2-keto-D-glucose dehydrogenase from Pseudomonas aureofaciens (7) and pyranose dehydrogenase from C. cinerea (8) were all characterized as novel PQQ-dependent enzymes. Free PQQ has been identified in a wide variety of foods (9) and milk (10). PQQ is an essential nutrient for proper growth and development in mice (11). The strong-antioxidant capacity of PQQ protects living cells and biomolecules from oxidative stress in vivo and in vitro (12, 13). Furthermore, PQQ exerts a protective effect against ultraviolet irradiation-induced human dermal fibroblast senescence in vitro (14) and suppresses the serum low density cholesterol level to prevent various diseases (15). In addition, PQQ may improve skin conditions and slow the progression of osteoarthritis (16).The chemical structure of PQQ was determined in 1980 (17). Since then gene clusters involved in the synthesis of PQQ from different bacteria that range from 4 genes ...